Ocean acidification is the multidecadal decrease in ocean pH and change in seawater inorganic carbon chemistry caused primarily by uptake of anthropogenic carbon dioxide (CO2) from the atmosphere. Global surface ocean mean pH has decreased from 8.2 to 8.1 over the past two centuries; the current pH decrease is about 10-100 times faster than past trends observed in the recent geological record. As CO2 dissolves into the ocean, it decreases pH as well as carbonate ion concentrations (CO32–). Carbonate ions are required for the hard calcium carbonate (CaCO3) shells and skeletons that many marine organisms create. Many organisms decrease their rate of CaCO3 production in response to ocean acidification. Other biological responses to ocean acidification include changes in photosynthesis and respiration, alterations in behavior, and shifts in intracellular chemistry. Ocean acidification may also alter the biogeochemical cycling of nitrogen, carbon, and micronutrients. Direct impacts on individual organisms could then indirectly affect local ecosystems via altered predator-prey relationships, competition, and habitat availability. Ecosystems that will most likely be affected include coral reefs, open ocean environments, high-latitude oceans, and deep-sea regions. Susceptible species provide human communities with many goods and services, so human communities may feel the effects of ocean acidification in several ways.
Cooley S. R., Doney S. C., in press. Ocean acidification. Encyclopedia of Environmetrics. Article (subscription required).